It is desirable to transmit a large number of signals using fiber optic technology. However, it is extremely expensive and time consuming to provide a larger number of cables between transmitters and receivers. Thus, in order to transmit a large number of signals with existing hardware, a plurality of signals must be carried on each cable.
In order to transmit a large number of signals on a given cable, signals carried on a plurality wavelengths are multiplexed together for transmission. After the multiplexed signal reaches the destination, the signals are demultiplexed, in order to access the information carried on a single wavelength. Conventional wavelength division demultiplexer are used to separate the signal into individual wavelengths.
Conventional wavelength division multiplexers utilize a pair of filters in order to achieve high isolation which pass light in a range around a single wavelength to separate the signal into its component signals. The range of wavelengths transmitted by a filter is the pass band. Referring to FIG. 1, the pass band 11 is a narrow portion of the wavelength. Each of the component signals, centered a single wavelength, is known as a channel. However, each channel actually exists over a range of wavelengths.
As of number of channels increases, the channels must be placed closer together in order to carry the signals in the same total wavelength range. However, as the channels are placed closer together, the blocking bands begin to overlap. To remedy this, conventional systems pass each channel through at least two filters in series. Thus, the pass band is narrowed sufficiently to allow individual channels to be deconvoluted.
Although the conventional systems can separate signals on individual channels, those with ordinary skill in the art will realize that conventional systems also result in higher insertion loss. Each filter has a transmission loss associated with it. Consequently, the plurality of filters cause additional insertion loss. In addition, because a filter narrows the entire channel transmitted by the filter, the pass band is narrowed. Because the pass band is narrowed, the laser providing the signal for the channel must provide light within the narrower pass band. Consequently, a more accurate laser is also required.
Accordingly, what is needed is a system and method for providing a wavelength division multiplexer which has lower insertion loss and requires a less accurate laser. The present invention addresses such a need.